1. Field of the Invention
The present invention relates to a group communications switching method, and a subscriber terminal and a server used for the method. More particularly, the present invention relates to a group communications switching method, and a subscriber terminal and a server used for the method for switching between group communications and voice communications.
2. Description of the Related Art
OMA (Open Mobile Alliance) that is an industry organization of mobile communications standardizes group communications as “Push-to-Talk over Cellular (to be referred to as “POC” hereinafter) Phase One”. The POC is a kind of VoIP (Voice over Internet Protocol) for communicating voice over a data communications network using IP (Internet Protocol), and is developed for mobile communications. The POC uses the data communications network, and does not use a circuit switching scheme. The POC is a technology for realizing communications like those performed by a transceiver in which “push a button” and “talk”.
In the POC, without dialing the other party's telephone number that is necessary in the circuit switching scheme, the user of the POC selects the other parties and pushes a button so as to be able to connect to the parties within a few seconds. In addition to one-to-one communications, simultaneous connections among plural terminals that form a group is available in the POC.
In the POC, voice of a user who is pushing the button is sent to the grouped parties. A user who pushes the button first gets a right to talk where other users can only hear the voice. In addition, different from the circuit switching scheme, since the POC uses the data communications network, users can use the communications service at lower cost than that for conventional voice communications.
As a prior art, Japanese Laid-Open Patent Application No. 4-70226 discloses a cordless phone system in which a handset is connected to another handset via a dedicated channel. In the cordless phone system, when a switch is turned on while communications are being performed between two parties, group communications become available.
As another prior art, Japanese Laid-Open Patent Application No. 2002-16973 discloses a mobile communications system for performing conference communications in which group communications can be switched to communications between two parties by pushing a switching button when the two party communications become necessary.
Currently, according to the specification of POC, POC cannot be used concurrently with normal voice call, TV phone or data communications. For example, when POC call arrives while the normal voice communications or TV phone communications are being performed, the user needs to decide whether to continue the normal voice communications/TV phone communications or to end the normal voice communications/TV phone communications in order to start the POC.
When normal voice call or TV phone call arrives while the POC is being used, the user needs to decide whether to continue the POC call or to interrupt the POC to start the normal voice communications or TV phone communications. In either case, there is a problem in that the user needs to decide a service over a short amount of time.
In addition, in an existing service for switching the POC call to a normal circuit switching voice call, a connection of the normal voice call is established while POC is being performed. Then, when all users participating in a group of the POC complete the POC call, switching to the normal voice call completes. In this switching procedure, since it is necessary that other users end the POC, there is a problem in that switching cannot be completed quickly.